Video playback method and surveillance system using the same

ABSTRACT

A surveillance system and method are provided. The surveillance system includes a video capturing device and a processing device. The video capturing device obtains a video and generates metadata associated therewith. The metadata records a trajectory of an object appearing in the video. The processing device executes the video playback method, namely to obtain the metadata, define a section on the trajectory based on information of the trajectory, command a player to play the video by a first speed when the object appears on the section, and selectively command the player to play the video by a second speed when the object appears on the trajectory except the section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 103129946 filed in Taiwan, R.O.C. onAug. 29, 2014, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The disclosure relates to a video playback method and a surveillancesystem using the same, more particularly to a method and system fordeciding the play speed of a video according to a trajectory of anobject.

BACKGROUND

Usually the purpose for the playback of videos in a surveillance systemis to search for a certain person, object or event. If a time pointwhere a target object appears or occurs is unknown, users usually preferto fast forward the playback videos until finding the target object, andthen review them in slow motion. On a common playback user interface,users have to suspend the playback videos immediately when finding thetarget object, and then rewind the video or pull a slider backward tilla certain time point of the time line that the target object appears.

During the playback, each action to manually operate the surveillancesystem, such as pushing buttons, keyboard operation or mouse operation,requires a response time for the human brain to control the hands to dothe action in response to visional stimulation. Therefore, such a humanresponse time may not fit in the playback of videos on a machine,especially when users operate the interface wrongly or with confusion.For example, when a user reactively suspends the playback, the playbackprogress herein may exceed a desired play time point, resulting in thatthe user must rewind the video to search for the target object again. Ifforgetting to slow down the playback, the user herein has to rewind thevideo to search for the target object again. However, no one wants torepeatedly rewind and search again and again until a clip of the videothat the target object can be observed clearly is found.

SUMMARY

According to one or more embodiments, the disclosure provides a videoplayback method. In one embodiment, the video playback method includesacquiring metadata that is associated with a video and records atrajectory of at least one object appearing in the video, defining asection on the trajectory according to information about the trajectory,playing the video by a first speed when the object appears on thesection of the trajectory and selectively playing the video by a secondspeed when the object appears on the trajectory except the section.

According to one or more embodiments, the disclosure also provides asurveillance system for video playback. In one embodiment, thesurveillance system includes a video capturing device and a processingdevice. The video capturing device captures the foregoing video andgenerates the foregoing metadata. The processing device is electricallyconnected to the video capturing device and performs the foregoing videoplayback method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only and thus are not limitativeof the present invention and wherein:

FIG. 1 is a block diagram of a processing system according to anembodiment of the disclosure;

FIG. 2 is a flow chart of a video playback method according to anembodiment of the disclosure;

FIGS. 3A to 3G are schematic diagrams of trajectories of an object in avideo according to various embodiments of the disclosure; and

FIG. 4 is a schematic diagram of a timeline of a video according to anembodiment of the disclosure.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawings.

Please refer to FIG. 1, which is a block diagram of a surveillancesystem 1 according to an embodiment of the disclosure. The surveillancesystem 1 includes a processing device 10 and a video capturing device12. The processing device 10 and the video capturing device 12 arecoupled to each other, and the processing device 10 is coupled to aplayer 14. In another embodiment, the player 14 is included in thesurveillance system 1. In another embodiment, the processing device 10,the video capturing device 12 and the player 14 are integrated into anapparatus or are separated.

The video capturing device 12 captures a video. In an embodiment, theterm “capture” means to record or capture sequential images of the realworld. The video capturing device 12 herein includes a camera lens andrelative modules. In another embodiment, the term “capture” means todownload or receive data from the outside of the surveillance system 1.The video capturing device 12 herein is a computer. After the video isobtained, the video capturing device 12 generates metadata associatedwith the video. Specifically, the video capturing device 12 is capableof analyzing the content of a video, recognizing at least one objectappearing in the video, and recording a trajectory of the at least oneobject into the metadata. Such an ability of video content analysis issupported by a video analytics engine defined by the open network videointerface forum (ONVIF) or by other types of video analytics engine. Inan example, the trajectory is recorded in a list, but the disclosurewill not be limited thereto. Each data in the list includes a time pointand a location of the object in a certain frame of the video at the timepoint. The time points are indicated by, for example but not limited to,timestamps, the number of each frame of the video, or other identifiersin a certain order. For example, each frame of a video has 800×600pixels, and the list recites an object appearing at a location with thecoordinate (x₁₆₁, y₁₆₁) in the 161^(st) frame of the video, wherein1≤x₁₆₁≤800 and 1≤y₁₆₁≤600. In another embodiment, the metadata furtherincludes the category, color and/or size of an object to be recognized.

The processing device 10 performs a video play back method to commandthe player 14 to playback the video. The processing device 10 is anytype of present or feature processor, central processing unit (CPU),control unit, microprocessor, microcontroller, certainapplication-specific integrated circuit, field-programmable gate array,complex programmable logic device, system-on-chip, system-in-package orany hardware component, which has the computing ability and is capableof performing instructions for the video playback method.

The video playback method is carried out by, for example but not limitedto, a computer program stored in a computer-readable storage medium sothat a computer can perform the video playback method after reading thecomputer program from the computer-readable storage medium. For instant,the computer-readable storage medium is, but not limited to, a read-onlymemory, a flash memory, a floppy disk, a hard disk drive, an opticaldisk, an USB drive, a magnetic tape or other storage mediums having thesame function.

Please refer to FIG. 1 and FIG. 2 which is a flow chart of a videoplayback method according to an embodiment of the disclosure. As shownin step (a), the processing device 10 acquires the metadata. In step(b), the processing device 10 defines a section (referred to as aninterest section) on the trajectory of the object according to theinformation of the trajectory of the object in the metadata. Such aninterest section of the trajectory is associated with the commands whichthe processing device 10 sends to the player 14 in steps (c) and (d).

In step (c), the processing device 10 commands the player 14 to play thevideo by the first speed when the object appears on the section of thetrajectory. The first speed is related to a second speed so that theplayer 14, according to the commands provided by the processing device10, plays different portions of the video by two different speeds,respectively. In an embodiment, the first speed is slower than thesecond speed. When the video is played by the second speed (i.e. therelative fast play), the processing device 10 defines a time period forplaying the video by the first speed (i.e. the relative slow playback).Therefore, the user may clearly observe an object of interest appearingon the interest section of the trajectory during the defined timeperiod.

In another embodiment of the step (c), the processing device 10 merelyappoints a certain section of the trajectory or the trajectory exceptthe certain section and informs the player 14 about a specific task ofthe appointed part of the trajectory or the time period of the relativeslow playback instead of appointing the first or second speed.Therefore, the player 14 can realize the definition of the appointedpart of the trajectory and play the frames of the video which the objectappears on the interest section of the trajectory, by a certain way(e.g. the first speed) and the reset of frames of the video by anotherway (e.g. the second speed) after receiving such commands from theprocessing device 10.

In step (d), the processing device 10 specifically commands the player14 to play the video by the second speed when the object appears on thetrajectory except the section. The step (d) is optionally performed. Inan example, the above object is referred to as a first object and thepriority of step (c) is higher than the priority of step (d) so thatwhen another object (referred to as a second object) appears, theprocessing device 10 defines an interest section on a trajectory of thesecond object in step (b). When the first object leaves from theinterest section of its trajectory in the video, the player 14 plays thevideo by the second speed according to the command in step (d)corresponding to the first object. Meanwhile, the second object appearson the interest section of its trajectory in the video, so the player 14should play the video by the first speed according to the command instep (c) corresponding to the second object. However, such two commandsin steps (c) and (d) are incompatible with each other, so the command instep (c) will be selected. In other words, whenever an object appears onthe interest section of its trajectory in the video, the player 14 willplay the video by the first speed. When all objects appearing in thevideo leave from their interest sections in step (d), the player 14 willplay the video by the second speed.

The processing device 10 may specifically command the player 14 throughtheir connection. In an embodiment, the player 14 is separated from thesurveillance system 1 so the processing device 10 may not know theexistence of the player 14 (i.e. lack of the connection between theprocessing device 10 and the player 14 as shown in FIG. 1). Accordingly,if any device obtains the information about the interest section storedin the metadata or other files, this device can display the videoaccording to the obtained information. The steps (c) and (d) areperformed based on the standard in the art in an embodiment or based onthe communication scheme between the processing device 10 and theunknown player 14, such as a certain data format or protocol.

On the other hand, the player 14 receives the video from the processingdevice 10 or from the video capturing device 12 (if coupled to the videocapturing device 12) or receives the metadata or non-appointed commandsfrom the video capturing device 12 or the processing device 10. In anexample, the player 14 is a computer including a module capable ofdisplaying or outputting frame images, and these displayed or outputframe images may present a playing interface. In another example, theplayer 14 includes a physical interface module. Moreover, the player 14plays the video forward or backward according to the received commands.

The step (b) is performed based on the information about the trajectoryof the object (hereinafter referred to as the trajectory information ofthe object), and this trajectory information is derivative data of thetrajectory recorded in the metadata. The following one or moreembodiments will, by referring the foregoing drawings, illustrate how todefine one or more interest sections of the trajectory presented in thevideo played by the first speed.

Please refer to FIG. 3A, which is a schematic diagram of a trajectory 3a of an object on a video according to an embodiment of the disclosure.The object appears at a location P0 in the video and disappears at alocation P9 in the video. The trajectory information includes spaces orlocations of the object at multiple time points so that the processingdevice 10 can define at least one interest section according to thisinformation and control the player 14 to play the video by the firstspeed when the object enters into or leaves this interest section. Forexample, the sections S1 and S9 shown in the drawing are set as interestsections.

In an embodiment, when the object appears on the sections S1 and S9, theplayer 14 plays the video by the same first speed or by different firstspeeds which respectively correspond to the sections S1 and S9. In anembodiment, the first speed corresponding to the section S1 or S9 is aconstant value or a variable value. For example, assume the fast play ofthe video is under the second speed and the slow play of the video isunder the first speed. Then, when the object moves from the location P0to the location P1, the video is played by the first speed that isgradually increasing from a minimum value at the location P0 to thesecond speed at the location P1.

In an embodiment, the processing device 10 merely marks the interestsections, the details of playing the video are defined by the player 14or users. The disclosure will have no limitation on the lengths of thesections S1 and S9.

Please refer to FIG. 3B, which is a schematic diagram of a trajectory 3b of an object on a video according to an embodiment of the disclosure.Similar to the object in FIG. 3A, an object in FIG. 3B appears at thelocation P0 and disappears at the location P9 in the video. Theprocessing device 10 estimates a middle point M50 of the trajectory 3 bin length according to a plurality of locations of the object in thevideo and defines an interest section extending from the middle pointM50. This interest section includes the middle point M50.

In an embodiment, the middle point M50 is at the central of the interestsection. In another embodiment, the interest section is a section SM50that extends by a certain length from the middle point M50 toward thelocation P9 along the trajectory 3 b. In another embodiment, theinterest section is a portion of the trajectory 3 b, which extends by acertain length from the middle point M50 toward the location P1 alongthe trajectory 3 b. In an embodiment, the interest section is a portionof the trajectory 3 b, which extends by a first length from the middlepoint M50 toward the location P1 and also extends by a second lengthfrom the middle point M50 toward the location P9 along the trajectory 3b, and the first length and the second length are different.

The trajectory 3 b includes one or more middle points. In an embodiment,the above middle point M50 is a special case among the middle points ofthe trajectory 3 b. In another embodiment, the middle point is a certainequipartition point of the trajectory 3 b in length, e.g. a trisectionpoint M66. In another embodiment, the middle point is any point of thetrajectory 3 b.

In this way, according to such one or more middle points, the processingdevice 10 can define one or more interest sections for playing the videoby the first speed.

In order to simplify the selection of the one or more middle points, aframe can be divided into a plurality of regions, and an interestsection of a trajectory in step (b) can be defined according to one ofthe regions of the frame. Please refer to FIG. 3C, which is a schematicdiagram of a trajectory 3 c of an object on a video according to anembodiment of the disclosure. A frame of the video is at least dividedinto three regions A10, A20 and A30. In the metadata, the informationabout the section S10 corresponds to the information about the regionA10, and the information about the section S30 corresponds to theinformation about the region A30. Accordingly, the trajectoryinformation can be simplified.

Each of the location of the object has a corresponding time point inFIG. 3B. Please refer to FIG. 3D, which is a schematic diagram of atrajectory 3 d of an object on a video according to an embodiment of thedisclosure. In this embodiment, the trajectory 3 d includes a pluralityof time points. An object appears in the video at a time point 0.0 anddisappears at a time point 9.0. The processing device 10, according tothe time points, estimates a location T50 of the object corresponding toa middle time point 4.5 and then defines a section ST50 covering thelocation T50 according to the locations of the object corresponding tothe time points on the trajectory 3 d. The middle time point 4.5 is aspecial case among the one or more middle time points related to thetrajectory 3 d. The middle time point can be a certain equipartitiontime point related to the trajectory 3 d. For example, the middle timepoint is a trisection time point 3.0 or 6.0 or is any time point relatedto the trajectory 3 d, such as a time point 8.0. In FIG. 3A or 3C, theprocessing device 10 selects a middle time point that the object justappears or disappears on the screen, and then defines an interest timeperiod, such as a time period ST85 of 1.0 (i.e. 9.0−8.0=1.0) unit timewhich is a final period that the object exists in the video.

Please refer to FIG. 3E, which is a schematic diagram of a trajectory 3e of an object on a video according to an embodiment of the disclosure.This embodiment in FIG. 3E is a combination of the embodiments in FIGS.3B and 3D. That is, the processing device 10 estimates a middle pointaccording to the locations of the object weighted by time points. InFIG. 3E, the trajectory 3 e has a spatial length of 9 units, where thereis an interval of 1 unit between the locations P0 and P1, between thelocations P1 and P2, between the locations P2 and P3, between thelocations P3 and P4, between the locations P4 and P5, between thelocations P5 and P6, between the locations P6 and P7, between thelocations P7 and P8, and between the locations P8 and P9. The objectmoves along the trajectory 3 e by non-uniform motion according to thetime points 0.0 to 9.0. Therefore, a middle point of the trajectory 3 eweighted is an unit distance of 3.1 (i.e.0.5×(3.0−0.0)+1.5×(4.0−3.0)+2.5×(5.0−4.0)+3.5×(6.0−5.0)+4.5×(6.5−6.0)+5.5×(7.5−6.5)+6.5×(8.0−7.5)+7.5×(8.5−8.0)+8.5×(9.0−8.5)]÷9.0≈3.1)away from the location P0 and is a location P31 between the locations P3and P4. According to the information of the middle point P31, theprocessing device 10 defines an interest section of the trajectory 3 e,and this interest section is related to a position in screen where theobject averagely took a longest time on traveling. In view of thelocations P0 to P9, a part of the trajectory 3 e that the object movesthe slowest in the video, is defined as an interest section and isbetween the locations P0 and P1 and corresponds to 3.0 (i.e.3.0−0.0=3.0) unit time in an embodiment. In another embodiment, theweighted calculation of middle points is carried out by other weightarrangement methods, such as enhancing the weight of an importantlocation or the weight of an important time point.

Please refer to FIG. 3F, which is a schematic diagram of a trajectory 3f of an object on a video according to an embodiment of the disclosure.When the processing device 10 under the video playback method detectsthat the trajectory 3 f at least overlaps a part of a region A28 of aframe, the step (b) is performed.

The region A28 is defined by a various ways. In an embodiment, theregion A28 is a region of interest so that the processing device 10defines a part of the trajectory 3 f covered by the region A28 to be aninterest section, i.e. a section S28. In another embodiment, a regionA25 of a frame is set as a region of interest that is smaller than theregion A28 and slightly overlaps or does not overlap the trajectory 3 f,so that the processing device 10 defines a section S28 of the trajectory3 f that is close to the region A25, to be an interest section. Herein,the term “close to” indicates that a part of the trajectory 3 f has aspace, which is equal to or less than a buffer distance d3, with theregion A25. In another embodiment, the location P22 is a location ofinterest so that the processing device 10 defines a section S28 of thetrajectory 3 f which is close to the location P22, to be an interestsection. Herein, the term “close to” indicates that a part of thetrajectory 3 f has a space that is equal to or less than a bufferdistance d6, with the location P22. In another embodiment, the regionA28 is a region of interest so that the processing device 10 defines thetrajectory 3 f except a section S28 to be an interest section, i.e. asection S72.

As set forth above, the processing device 10 performs the step (b)according to at least one of the foregoing considerations for atrajectory. In one dimension, a trajectory is indicated with points orlocations, by referring to the embodiments shown in FIGS. 3B, 3C, 3D and3E.

Moreover, the trajectory information includes a direction, length,pattern or other characteristics of the trajectory. In an embodimentbased on the trajectory 3 a, the interest section defined by theprocessing device 10 has directionality. For example, the section S6 inFIG. 3A extends toward the upper side of the drawing.

In addition, a part of the trajectory matching a certain condition suchas length or pattern is defined as an interest section for the player 14to play the video by the first speed when the object appears on theinterest section.

However, the interest section corresponds to a part or the whole of timeduring which the object appears in the video. Please refer to FIG. 3G,which is a schematic diagram of a trajectory 3 g of an object on a videoaccording to an embodiment of the disclosure. An object appears at alocation P0 in the video at a time point 0.0 and disappears at alocation P9 in the video at a time point 9.0. In this embodiment, thereare a preset region A15 and a preset region A35 on the frame. In thevideo playback method, the processing device 10 detects that thetrajectory 3 g overlaps at least a part of the region A15 and a part ofthe region A35.

When the object first appears in the region A15 at a time point 3.0 andthen enters into the region A35 at a time point 8.5, the processingdevice 10 performs the step (b). In other words, when the trajectory 3 gcrosses the regions A15 and A35 and the pattern of the trajectory 3 gsubstantially matches a pattern D having directivity, the step (b) isperformed. In an example, the video capturing device 12 is asurveillance camera installed among public areas (e.g. the region A15)and private areas (e.g. the regions A35 and A45) in a company. Ingeneral, a human-shaped object traveling in the private regions A35 andA45 should be a reliable employee. Once a guest enters into the privateregion A35 from the public region A15 without any authorization and maydamage the company security, it is necessary for the company to play asurveillance video by a first speed in order to monitor the trajectory(e.g. the trajectory 3 g) of every human-shaped object, especially tomonitor a section of the trajectory in which an entrance guard is set.

In some embodiments, there are more preset regions set in the screen,and these regions to visit can be arranged in a certain order accordingto actual application requirements in order to set the basis ofperforming the step (b).

In an embodiment, a part of a trajectory formed by a specific objectthat belongs to a specific category or has a specific color or size, isset as an interest section. For example, the processing device 10 canperform the video processing to a trajectory formed by a specific humanhaving a certain skin color or stature, rather than to trajectoriesformed by other objects except the human, such as a car.

In an embodiment, a certain section of a trajectory matching a specificcondition is set as an interest section if an object appears thereon.For example, the video capturing device 12 can recognize human faces,the metadata has relative information, and the processing device 10 canaccordingly command that the video is played by the first speed when anyobject is recognized as having a human face.

Please refer to FIGS. 1 and 2 and FIG. 4, which is a schematic diagramof a timeline of a video according to an embodiment of the disclosure. Afirst object appears between a time point t₁₀ and a time point t₁₉, Asecond object appears between a time point t₂₀ and a time point t₂₉, anda third object appears between a time point t₃₀ and a time point t₃₉.

In an embodiment, the processing device 10 defines an interest timeperiod between a time point t₁₄ and a time point t₁₈ according to a timepoint t₁₆ corresponding to a middle point of a trajectory of the firstobject. The time point t₁₄ overlaps the time point t₁₆, and the value ofthe time point t₁₈ is the value of the time point t₁₆ plus a certainvalue. In another embodiment, the processing device 10 defines aninterest time period between a time point t₃₄ and a time point t₃₈according to a time point t₃₆ corresponding to a middle point of atrajectory of the third object. The value of the time point t₃₄ is thevalue of the time point t₃₆ minus a certain value, and the value of thetime point t₃₈ is the value of the time point t₃₆ minus another certainvalue. In another embodiment, the processing device 10 defines aninterest time period between a time point t₂₄ and a time point t₂₈according to any time point, e.g. a time point t₂₆, corresponding to anymiddle point of a trajectory of the second object. In anotherembodiment, the processing device 10 defines an interest time periodbetween the two time points t₂₄ and t₂₈ according to none of the middlepoints of the trajectory of the second object.

In an embodiment, the time period between the time points t₁₈ and t₁₄,the time period between the time points t₂₈ and t₂₄, and the time periodbetween the time points t₃₈ and t₃₄ are equal to or less than a timeperiod threshold so that the time period for playing the video by thefirst speed will be limited. For the first object, such a time periodthreshold is equal to the certain value for estimating the interest timeperiod according to the time point t₁₆. For the third object, a half ofthe time period threshold is equal to the certain value for estimatingthe interest time period according to the time point t₃₆. The step (c)may be performed earlier than the step (d), so the video is played bythe first speed during the time period between the time points t₁₆ andt₂₈ and during the time period between the time points t₃₄ and t₃₈ onthe time line t. The time period between the time points t₁₆ and t₂₈ isslightly longer than the time period between the time points t₁₄ and t₁₈defined according to the trajectory of the first object, and is slightlylonger than the time period between the time points t₂₄ and t₂₈ definedaccording to the trajectory of the second object.

Therefore, this may provide an enough time for users to clearly observemultiple objects (e.g. the first and second objects).

What is claimed is:
 1. A video playback method for object tracking in asurveillance system, comprising steps of: (a) acquiring metadata that isassociated with a video and records a trajectory of at least one objectappearing in the video; (b) detecting whether the trajectory at leastoverlaps a part of a preset region, and predefining a middle point onthe trajectory and in the present region and defining a section of thetrajectory based on the middle point according to the metadata when thetrajectory at least overlaps the part of the preset region; (c)commanding that the video is played by a first speed when it isdetermined according to the metadata that the object appears on thesection of the trajectory; and (d) selectively commanding that the videois played by a second speed when it is determined according to themetadata that the object appears on the trajectory except the section.2. The video playback method according to claim 1, wherein theinformation about the trajectory comprises a plurality of locations ofthe object on the trajectory in the video and a timestamp correspondingto each of the locations of the object, the section of the trajectorycomprises at least one middle point of the trajectory, the step (b) isperformed based on the at least one middle point, and the processingmethod further comprises: defining the at least one middle pointaccording to the timestamps.
 3. The processing video playback methodaccording to claim 1, wherein the information about the trajectorycomprises a plurality of locations of the object on the trajectory inthe video and a timestamp corresponding to each of the locations of theobject, the section of the trajectory comprises at least one middlepoint, the step (b) is performed based on the at least one middle point,and the processing method further comprises: defining the at least onemiddle point according to the locations of the object.
 4. The videoplayback method according to claim 1, wherein the information about thetrajectory comprises a direction, length or pattern of the trajectory,which the step (b) is based on.
 5. The video playback method accordingto claim 1, wherein the step (b) is performed when the trajectory atleast partially overlaps at least a region of a frame of the video. 6.The video playback method according to claim 1, wherein a frame of thevideo comprises at least one first region and at least one secondregion, and the step (b) is performed when the trajectory at leastpartially overlaps the first region and the second region and the objectappears to the first region and then appears to the second region. 7.The video playback method according to claim 1, wherein the section ofthe trajectory comprises at least one middle point of the trajectory,and the step (b) is performed according to a time period threshold thatis associated with the at least one middle point which the objectappears at.
 8. The video playback method according to claim 1, whereinthe first speed is slower than the second speed.
 9. A surveillancesystem for object tracking by video playback, comprising: a videocapturing device, for capturing a video and generating metadataassociated with the video, and the metadata recording a trajectory of atleast one object appearing in the video; and a processing device,electrically connected to the video capturing device and configured toperform steps of: (a) acquiring the metadata; (b) detecting whether thetrajectory at least overlaps a part of a preset region and predefining amiddle point on the trajectory and in the present region and defining asection of the trajectory based on the middle point according to themetadata when the trajectory at least overlaps the part of the presetregion; (c) commanding that the video is played by a first speed when itis determined according to the metadata that the object appears on thesection of the trajectory; and (d) selectively commanding that the videois played by a second speed when it is determined according to themetadata that the object appears on the trajectory except the section.10. The surveillance system according to claim 9, further comprising: aplayer, electrically connected to the processing device and configuredto play the video according to commands of the processing device. 11.The surveillance system according to claim 9, wherein the informationabout the trajectory comprises a plurality of locations of the object onthe trajectory in the video and a timestamp corresponding to each of thelocations of the object, the section of the trajectory comprises atleast one middle point of the trajectory, the step (b) is performedbased on the at least one middle point, and the processing methodfurther comprises: defining the at least one middle point according tothe timestamps.
 12. The surveillance system according to claim 9,wherein the information about the trajectory comprises a plurality oflocations of the object on the trajectory in the video and a timestampcorresponding to each of the locations of the object, the section of thetrajectory comprises at least one middle point, the step (b) isperformed based on the at least one middle point, and the processingmethod further comprises: defining the at least one middle pointaccording to the locations of the object.
 13. The surveillance systemaccording to claim 9, wherein the information about the trajectorycomprises a direction, length or pattern of the trajectory, which thestep (b) is performed based on.
 14. The surveillance system according toclaim 9, wherein the step (b) is performed when the trajectory at leastpartially overlaps at least one region of a frame of the video.
 15. Thesurveillance system according to claim 9, wherein a frame of the videocomprises at least one first region and at least one second region, andthe step (b) is performed when the trajectory at least partiallyoverlaps the first region and the second region and the object appearsto the first region and then appears to the second region.
 16. Thesurveillance system according to claim 9, wherein the section of thetrajectory comprises at least one middle point of the trajectory, andthe step (b) is performed according to a time period threshold that isassociated with the at least one middle point which the object appearsat.
 17. The surveillance system according to claim 9, wherein the firstspeed is slower than the second speed.